This project continues a detailed investigation of an hepatotoxic metabolite, rubratoxin B, elaborated by a food-storage fungus, Penicillium rubrum. Its molecular toxicity will be ascertained in susceptible animals and its pathological effects noted to determine the molecular mechanism(s) of action. Biochemical investigations will be undertaken to determine metabolic alterations, i.e., changes in enzyme activity. Effects on isolated tissue, cells and particulate fractions (mitochondria, lysosomes, microsomes) will be examined. Such knowledge of effects of rubratoxin B on an enzyme(s), transport system, or hormone system would assist greatly in constructing a picture of the events when whole animals are poisoned by the compound. The reactivity of rubratoxin in an animal organism will be studied by examining its metabolic products. Such studies will employ classical toxicological methods and radiolabeled rubratoxin. After identification of the metabolic products, the enzymic mechanisms by which these metabolites are produced will be examined. In addition to studies with rubratoxin, other mycotoxins (ochratoxin, penitrem A, aflatoxin) will be examined to determine the effects of multiple exposure. Since mycotoxins are rarely found singly in nature, studies of multiple exposures to one or two agents by feeding to pregnant rats and administration to neonatal pups in maximally tolerated doses will be undertaken. Toxicological investigations to determine metabolic alterations such as changes in exzyme activity and changes in cellular respiration will be examined. With this knowledge the causal chain of events leading to death or illness can be examined. The metabolic reactions which modify the toxicity of the mycotoxin and its effect on the mechanism of toxicity can then be considered. It is hoped to obtain some idea of the contribution of these metabolic reactions in increasing or decreasing the toxicity of the compound. It is only by knowing the mechanism of toxicity that an intelligent approach to eliminating or, at least, decreasing toxic hazards can be undertaken. BIBLIOGRAPHIC REFERENCES: Hayes, A.W. 1976. Effect of aflatoxin B1 and rubratoxin B on bacteriophage and rabbit cornea cells. Bull. Environ. Contamin. Toxicol. 16. Watson, S.A. and A.W. Hayes. l976. Effect of mycotoxins singly or in combination on neonate rats. Toxicol. Appl. Pharmacol. 36.